JPH07114262A - Developing device - Google Patents

Abstract

PURPOSE:To reduce toner consumption and waste toner and, further, to prevent scattering of toner in a machine by setting a bias, which is applied to a second carrying means, to 0V, or setting the polarity to the reverse polarity of the electrification potential of a photoreceptor and also setting the absolute value of the potential to one which is smaller than the absolute value of the potential of the photoreceptor obtained after exposure. CONSTITUTION:The one-component magnetic toner 28 carried to a developing roller 22 by a toner replenishment roller 25 attracts to the roller 22 by a magnetic force. The roller 22 rotates in a direction shown by an arrow and the toner 28 is rubbed by a developing blade 24, so that it is frictionally electrified and, at the same time, formed into a thin layer. The electrified toner 28 is moved to an intermediate developing roller 23 by an electrostatic force, is carried onto a photosensitive drum 21, a part where a latent image is developed, and is developed by a potential difference between the roller 23 and the drum 21. Here, unnecessary toner development is prevented, by setting the bias which is applied to the roller 23 before the start of printing to 0V, or by setting the polarity to the reverse or same polarity of the electrification potential of the drum 21 and also setting the absolute value of the potential to one which is smaller than the absolute value of the potential of the drum obtained after exposure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device applied to an image forming apparatus such as a facsimile, a copying machine, a printer, etc., which uses an electrophotographic system.

[0002]

2. Description of the Related Art FIG. 6 is a block diagram of a developing device of a two-stage developing belt system, in which reference numeral 1 denotes a drum-shaped photosensitive member which is rotationally driven while an electrostatic latent image is formed. A developing device 9 is provided in the section. The developing device 9 includes a developing roller 2 serving as a first conveying unit that conveys the one-component magnetic toner 8, a developing blade 4 having its tip abutted against the developing roller 2, and the one-component magnetic toner 8 to the developing roller 2. The toner replenishing roller 5 for feeding the toner, the intermediate developing belt 3 as a second carrying means for carrying the toner, and the rollers 6, 7 for rotating the intermediate developing belt 3. A power source 10 for toner transfer bias is connected to the developing roller 2 and is applied with a bias Vd (V). Also,
A bias Vm (V) is also applied to the intermediate developing belt 3 by the developing bias power source 11.

FIG. 7 is a block diagram of a developing device of a two-stage developing roller system, in which an intermediate developing roller 12 is provided instead of the intermediate developing belt 3 shown in FIG. Other than that, the configuration is similar to that of FIG. 6, and the one-component magnetic toner 8 sent to the developing roller 2 by the toner replenishing roller 5 is attracted to the developing roller 2 by magnetic force. The developing roller 2 rotates in the direction of the arrow, and the one-component magnetic toner 8 is rubbed by the developing blade 4 to be triboelectrically charged and at the same time thinned. The charged one-component magnetic toner 8 is electrostatically transferred to the intermediate developing roller 12 which is the toner second conveying means, and is conveyed to the place where the latent image on the photoconductor 1 is developed. It is selectively transferred to the photoconductor 1 depending on the relationship with the surface potential. For example, when the toner is negatively charged and negative and positive development is performed, {(photoconductor potential)-
(Bias of the intermediate developing roller)} is positively developed.

[0004]

In the electrophotographic apparatus to which the above-mentioned developing device is applied, at the start of printing (at the time of printing the first sheet), the portion between the charger and the developing device on the photoconductor is Not charged. For this reason, the toner is solidly black-developed in a portion unrelated to the image.

Further, in a device using a semiconductor laser in an optical writing system, output control called APC is performed in order to prevent the output of the semiconductor laser from changing with the temperature of the semiconductor. In this method, a semiconductor laser is caused to emit light between pages and the output value is fed back to control the current flowing through the semiconductor laser.
At this time, since the photoconductor is exposed between pages, the toner is solidly black developed.

These toners are unnecessary toners for copying, and the toner consumption increases, and at the same time, most of the toners are collected in the cleaning unit, which leads to an increase in discharged toners. Further, it causes the toner to be scattered inside the machine.

An object of the present invention is to provide a developing device capable of reducing the toner consumption and the discharged toner by eliminating the above-mentioned unnecessary development of toner and preventing the scattering of toner inside the machine. Especially.

[0008]

SUMMARY OF THE INVENTION To achieve the above objects, the present invention is a method of charging 1 charged by friction or charge injection.
A first conveying means for conveying the component-based high resistance toner;
In the electrophotographic developing device having the second conveying means for receiving the toner from the first conveying means and developing the latent image on the photoconductor, the bias applied to the second conveying means before the start of printing is 0V. Or the polarity opposite to the charging potential of the photoconductor, or the same polarity as the charging potential and the absolute value of the potential is set smaller than the absolute value of the photoconductor potential after exposure.

Further, the difference between the bias applied to the first carrying means and the bias applied to the second carrying means at the time of printing, the bias applied to the first carrying means and the bias applied to the second carrying means before the start of printing. It is characterized in that each bias is switched so as to be equal to the difference of.

Further, a first conveying means for conveying the one-component high-resistance toner charged by friction or charge injection, and a toner for receiving the toner from the first conveying means to develop a latent image on the photosensitive member. In the electrophotographic developing device having the second transporting means, the bias applied to the second transporting means between pages is 0 V, or the polarity opposite to the charging potential of the photoconductor, or the same polarity as the charging potential and the potential. Is set to be smaller than the absolute value of the photoconductor potential after exposure.

The difference between the bias applied to the first conveying means and the bias applied to the second conveying means at the time of printing, and the bias applied to the first conveying means and the bias applied to the second conveying means between pages. The feature is that each bias is switched so that the difference becomes equal.

Further, a first conveying means for conveying the one-component high-resistance toner charged by friction or charge injection, and a toner for receiving the toner from the first conveying means to develop a latent image on the photosensitive member. In the electrophotographic developing apparatus having the second transporting means, the bias applied to the second transporting means before the start of printing and between pages is 0 V or the polarity opposite to the charging potential of the photoconductor or the charging potential. It is characterized in that the polarity and the absolute value of the electric potential are set smaller than the absolute value of the photosensitive member electric potential after exposure.

Further, the difference between the bias applied to the first conveying means and the bias applied to the second conveying means during printing, the bias applied to the first conveying means before the start of printing and between pages, and the second conveying means. It is characterized in that each bias is switched so that the difference from the applied bias becomes equal.

Further, the second conveying means is belt-shaped or roller-shaped.

[0015]

According to the above means, the bias applied to the second conveying means before the start of printing is 0 V, or the polarity opposite to the charging potential of the photosensitive member, or the same polarity as the charging potential and the absolute value of the potential is not. By setting the photoconductor potential after exposure to be smaller than the absolute value, unnecessary development of toner is eliminated.

Further, the difference between the bias applied to the first conveying means and the bias applied to the second conveying means at the time of printing, the bias applied to the first conveying means and the bias applied to the second conveying means before the start of printing. By switching each bias so that the difference becomes equal to, the unnecessary toner development is eliminated.

Further, the bias applied to the second conveying means between pages is 0 V, or the polarity opposite to the charging potential of the photoconductor, or the same polarity as the charging potential and the absolute value of the potential is the photoconductor potential after exposure. By setting it smaller than the absolute value of
Unnecessary toner development is eliminated.

Further, the difference between the bias applied to the first conveying means and the bias applied to the second conveying means during printing, and the bias applied to the first conveying means and the bias applied to the second conveying means between pages. By switching each bias so that the difference becomes equal, unnecessary toner development is eliminated.

The bias applied to the second conveying means before the start of printing and between pages is 0 V, or the polarity opposite to the charging potential of the photoconductor, or the same polarity as the charging potential and the absolute value of the potential after exposure. By setting it to be smaller than the absolute value of the photoconductor potential, the unnecessary toner development is eliminated.

Further, the difference between the bias applied to the first conveying means and the bias applied to the second conveying means at the time of printing, the bias applied to the first conveying means before the start of printing and between pages, and the second conveying means. By switching each bias so that the difference with the applied bias becomes equal, unnecessary toner development is eliminated.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a developing device according to an embodiment of the present invention. Reference numeral 21 is a photosensitive drum that is rotationally driven while an electrostatic latent image is formed. Is provided with a developing device 29. The developing device 29 may be of any type as long as it is used for developing the one-component high resistance toner (one-component magnetic toner) 28. In this embodiment,
A developing roller 22 as a toner first conveying means having a magnetic pole on the surface, a developing blade 24 having its tip abutted against the developing roller 22, and a toner replenishing roller 25 for sending the one-component magnetic toner 28 to the developing roller 22. It consists of and.

Between the developing roller 22 and the photosensitive drum 21,
There is an intermediate developing roller 23 as a toner second conveying means having elasticity, and the photosensitive drum 21 and the developing roller 22 have a contact nip due to elastic deformation of the intermediate developing roller 23.

A first high voltage power source 26 for toner transfer bias is connected to the developing roller 22 and is applied with a bias Vd (V). A second high-voltage power supply 27 for toner transfer bias is connected to the intermediate developing roller 23, and a bias Vm (V) is applied. Both the first high voltage power supply 26 and the second high voltage power supply 27 can switch the bias Vd and Vm by a signal from a CPU (not shown) that controls the developing device 29.

Next, the operation of this embodiment having the above construction will be described. The rotation direction of each roller is not limited to this embodiment.

The one-component magnetic toner 28 sent to the developing roller 22 by the toner replenishing roller 25 is magnetically attracted to the developing roller 22.
Adsorb to. The developing roller 22 rotates in the direction of the arrow, and the one-component magnetic toner 28 is rubbed by the developing blade 24 to be triboelectrically charged and at the same time thinned. 1 component magnetic toner charged 28
Is transferred to the intermediate developing roller 23 by electrostatic force, and the photosensitive drum
It is conveyed to the part where the latent image on 21 is developed. In the portion where the latent image on the photosensitive drum 21 is developed, the latent image is developed by the potential difference between the intermediate developing roller 23 and the photosensitive drum 21.

Here, FIG. 2 shows the relationship of each potential. Since the bias Vd of the developing roller 22 and the bias Vm of the intermediate developing roller 23 are set so that Vm-Vd> 0, the negatively charged toner is transferred from the developing roller 22 to the intermediate developing roller 23. The bias Vm of the intermediate developing roller 23 is the photoconductor charging potential Vp and the post-exposure potential V1 (V).
On the other hand, by setting Vp <Vm <V1 (<0), the toner is developed on the image black portion of the photoconductor drum 21 and is not developed on the image white portion. On the contrary, the bias Vm (V) of the intermediate developing roller 23 is Vp <V1
If it is set to be <Vm, the potential on the photoconductor is V1.
The development is not done even in the area of (V).

FIG. 3 shows a timing chart of the main motor driving the photoconductor and the developing device, the charger, the optical writing (semiconductor laser), the bias Vd of the developing roller 22 and the bias Vm of the intermediate developing roller 23. .

When copying is started, the main motor rotates, and at the same time, the charger is turned on to apply (bias +70) V to the intermediate developing roller 23 and (bias -1000) V to the developing roller 22. In the optical writing, the image information of the first page is written after performing the APC described above. The bias of the intermediate developing roller 23 is switched to −500V after Δt time has elapsed since the optical writing started writing the image information of the first page. The Δt time is because the position of the optical writing and the position of the developing device are deviated, and is not essential at all.

In optical writing, APC is also performed between the first and second pages. Between these pages, the bias of the intermediate developing roller 23 is switched to + 70V, and after the optical writing starts writing the image information of the second page, it is switched to -500V again after Δt time.

By switching the bias of the intermediate developing roller 23 as described above, unnecessary toner is removed from the photosensitive drum 21.
It is possible to prevent it from getting on.

FIG. 4 shows a developing roller 22 and an intermediate developing roller 23.
2 shows the relationship between the bias difference (Vm-Vd) and the toner adhesion amount m / a on the intermediate developing roller 23.

As the bias difference (Vm-Vd) increases, the toner adhesion amount m / a on the intermediate developing roller 23 increases, but when the bias difference (Vm-Vd) exceeds a certain amount, the intermediate developing roller 23 increases. On the contrary, the toner adhesion amount m / a on 23 decreases. As described above, the bias difference (Vm-Vd) and the toner adhesion amount m / a have a large relationship.

By the way, the toner adhesion amount m / a on the intermediate developing roller 23 has a great influence on the image density on the transfer paper. Therefore, the toner adhesion amount m / a on the intermediate developing roller 23 changes by switching the bias of the intermediate developing roller 23. As a result, the image density on the transfer paper changes, causing a problem of uneven image density.

However, by doing the following, it is possible to prevent the development of unnecessary toner and at the same time prevent the above-mentioned problems.

That is, as shown in the timing chart of FIG. 5, the timing for switching the bias (Vm) of the intermediate developing roller 23 is the same as in the example of FIG.
At the same time as switching the bias (Vm) of 23, the developing roller 2
The bias (Vd) of 2 is switched so that the bias difference (Vm-Vd) becomes constant. By doing so, it is possible to prevent the toner adhesion amount m / a on the intermediate developing roller 23 from changing due to the bias switching of the intermediate developing roller 23.

The same effect can be obtained by applying the two-stage developing belt system in which the intermediate developing roller 23 in the above-mentioned embodiment is replaced with the intermediate developing belt 3 described in FIG.

[0038]

As described above, according to the first, third and fifth aspects of the present invention, the developing device of the present invention eliminates unnecessary toner development, thereby reducing toner consumption and discharged toner. In addition, it is possible to reduce the amount of toner and prevent the toner from scattering inside the mansion.

According to the second, fourth, and sixth aspects of the present invention, in addition to the same effect as described above, uneven image density can be prevented.

According to the seventh and eighth aspects of the invention, the same effect as described above can be obtained even if the second conveying means has a belt shape or a roller shape.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a developing device of the present invention.

FIG. 2 is an explanatory diagram showing a potential of each part.

FIG. 3 is a timing chart of ON / OFF of each load and application of a bias.

FIG. 4 is a characteristic diagram showing a relationship between a bias difference between a developing roller and an intermediate developing roller and a toner adhesion amount on the intermediate developing roller.

FIG. 5 is a timing chart of bias application for preventing a change in toner adhesion amount.

FIG. 6 is a configuration diagram showing a developing device of a two-stage developing belt system.

FIG. 7 is a configuration diagram of a developing device of a two-stage developing roller system.

[Explanation of symbols]

21 ... Photosensitive drum, 22 ... Developing roller (first conveying means),
23 ... Intermediate developing roller (second conveying means), 24 ... Developing blade, 25 ... Toner replenishing roller, 26, 27 ... High voltage power source, 28 ... One-component magnetic toner (one-component high resistance toner),
29 ... Developer.

Claims (8)

[Claims] 1. Charged by friction or charge injection
A first conveying means for conveying the component-based high resistance toner;
In the electrophotographic developing device having the second conveying means for receiving the toner from the first conveying means and developing the latent image on the photoconductor, the bias applied to the second conveying means before the start of printing is zero volt. Or a polarity opposite to the charge potential of the photoconductor, or the same polarity as the charge potential, and the absolute value of the potential is set smaller than the absolute value of the photoconductor potential after exposure. 2. A difference between a bias applied to the first transport means and a bias applied to the second transport means during printing,
2. The developing device according to claim 1, wherein the biases are switched so that the difference between the bias applied to the first conveying means and the bias applied to the second conveying means before the start of printing becomes equal. 3. Charged by friction or charge injection
A first conveying means for conveying the component-based high resistance toner;
In an electrophotographic developing device having a second conveying means for receiving toner from the first conveying means and developing a latent image on a photoconductor, a bias applied to the second conveying means between pages is zero volt, Alternatively, the developing device is characterized in that the polarity is opposite to the charge potential of the photoconductor, or the same polarity as the charge potential and the absolute value of the potential is set smaller than the absolute value of the photoconductor potential after exposure. 4. A difference between a bias applied to the first transport means and a bias applied to the second transport means during printing,
4. The biases are switched so that the difference between the bias applied to the first transport unit and the bias applied to the second transport unit between pages becomes equal.
The developing device described. 5. Charged by friction or charge injection
A first conveying means for conveying the component-based high resistance toner;
In an electrophotographic developing device having a second conveying means for receiving toner from the first conveying means and developing a latent image on a photoconductor, a bias applied to the second conveying means before starting printing and between pages. Is set to zero volt, or the polarity opposite to the charging potential of the photoconductor, or the same polarity as the charging potential, and the absolute value of the potential is set smaller than the absolute value of the photoconductor potential after exposure. 6. A difference between a bias applied to the first transport means and a bias applied to the second transport means during printing,
6. The developing device according to claim 5, wherein the biases are switched so that the difference between the bias applied to the first transport unit and the bias applied to the second transport unit before the start of printing and between pages is equal. 7. The developing device according to claim 1, 2, 3, 4, 5 or 6, wherein the second conveying means is belt-shaped. 8. The developing device according to claim 1, 2, 3, 4, 5, or 6, wherein said second conveying means has a roller shape.